JPH0973067A - Method of driving optical modulator and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a device capable of optically modulating based on analog data by varying a voltage impressed to an optical modulation element of an optical modulation means according to gray scale information, and modulating a light signal during the time when a lighting time of a light source and an on-time of an optical modulation means overlap each other. SOLUTION: This device is constituted of an optical shutter 1 controlling light transmission as an optical modulation means, a light source 2 emitting light, a driving means DRI to drive the optical shutter, a driving means DR2 to turn on a light source 2 and a control means CONT to control power supply and operation timings of the two driving means. This constitution enables the device to vary the operation timing corresponding to the gray scale information when a voltage applied to the liquid crystal exceeds a threshold. When a gray scale information corresponding to the lowest level of the transmission state is inputted, the turn-off time of the light source 2 is set so that a transmission period (turn-on period) of the liquid crystal element and the turn-on period of the light source 2 do not overlap during the turn-on period of the light source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a method of driving an optical modulator and an image display device for controlling the amount of light transmitted or reflected from a light source.

[0002]

2. Description of the Related Art Optical modulators are used in various optical devices. For example, an optical modulation element of a display device. A liquid crystal display element will be described as the most familiar example. Conventionally, several methods have been proposed for performing gradation display using a liquid crystal element.

One is a method in which a twisted nematic liquid crystal (TN liquid crystal) is used as an optical modulation element (substance) and a voltage that changes according to gradation information is applied to the TN liquid crystal to modulate the transmittance of the entire pixel. Is.

[0004] Second, one pixel is configured as an aggregate of a plurality of sub-pixels, and each sub-pixel is turned on / off by binary data, thereby modulating the area of the light-transmitting sub-pixel. It is a method.

This method is disclosed in, for example, Japanese Patent Laid-Open No. 56-88193.
Publications, EP 453033 Publications, EP 361981
It is disclosed in Japanese Patent Publication No.

Thirdly, by making the intensities of the electric field distributed in one pixel or the inversion threshold of the liquid crystal different from each other, a portion showing a bright state and a portion showing a dark state in one pixel are divided. This is a method of modulating the area ratio of these portions by making them coexist.

This method is based on the "Ferroelectric Liquid Crystal Modulation Element (Ferroelectric Lithium) having a region in the pixel where nucleation and inversion occur in the pixel.
Quid crystal optical modu
relation device with regions
with in pixels to initia
te unification and inversi
U.S. Pat. No. 4,796,98
0, U.S. Pat. No. 4,712,877, U.S. Pat. No. 4,747,671, U.S. Pat. No. 4,763,994.
No. and the like.

The fourth is a method of modulating the length of a period in which one pixel is turned on and is in a bright state. This method was given to the inventor Kuribayashi et al., “Ferroelectric display panel and its gradation driving method (Ferroelectric display panel).
y panel and driving method
d therefor to active gray
US Pat. No. 4,70, entitled "scale)".
It is disclosed in the specification of No. 9,955.

Another example of digital duty modulation is the "Active Row Backlight Column Shutter Elsie Dee With One Shutter Transition", assigned to the inventor Nelson.
Purlow (Active row backlight
column shutter LCD with
one shutter transition pe
US Patent No. 5,311, entitled "r row)"
It is disclosed in the specification of No. 1,206.

Here, the first method is called luminance modulation, the second method is called pixel division, the third method is called domain modulation, and the fourth method is called digital duty modulation.

[0011]

Luminance modulation is difficult to apply to an element using an optical modulation substance having a characteristic in which the transmittance changes sharply with respect to an applied voltage or an optical modulation substance having a memory property.

In addition, luminance modulation is generally unsuitable for a system in which information changes at high speed because the response speed of TN liquid crystal is generally low.

Pixel division is the same as treating an aggregate of a plurality of pixels as a unit pixel, so that the spatial frequency is lowered and the resolution is apt to be lowered. Moreover, the area of the light-shielding portion increases and the aperture ratio decreases.

The domain modulation complicates the pixel structure for giving a distribution to the electric field strength and giving a distribution to the inversion threshold. Further, since the voltage margin for the halftone display is narrow, it is easily affected by the temperature.

In the digital duty modulation, since the ON / OFF time is modulated, the unit time of the modulation is limited by the clock frequency and the switching time of the gate, so that it is difficult to perform highly accurate modulation. That is, the multi-tone display has a limit. In addition, since it is necessary to always convert analog data to analog / digital (A / D) to obtain digital gradation information, it is difficult to apply the method to a simple system.

The present invention has been made in view of the above technical problems, and an object of the present invention is to provide an apparatus capable of optical modulation based on analog data.

Another object of the present invention is to provide an optical modulator and an image display device which can be applied to an optical modulator having a sharp applied voltage / transmittance characteristic and an optical modulator having a memory property.

Still another object of the present invention is to provide an optical modulator and an image display device which can achieve high resolution with high spatial frequency.

Another object of the present invention is to provide an inexpensive optical modulator and image display device capable of reproducing gradation information by analog duty modulation with a relatively simple system.

Still another object of the present invention is to provide an optical modulation device and an image display device which can perform excellent halftone display.

[0021]

Means for Solving the Problems The above-mentioned problems are solved,
Means for achieving the above-mentioned object is to change a voltage applied to an optical modulation element of the light modulation means in accordance with gradation information in a driving method of an optical modulation device having a light source and a light modulation means. The method for driving an optical modulator is characterized in that the overlap time of the ON time of the light modulating means and the lighting time of the light source is modulated.

The present invention also provides a method for driving an optical modulator having a light source, a light modulating means including a plurality of optical modulating elements or a planar optical modulating element, and a driving means for driving the light modulating means, The driving means modulates an overlap time between an ON time of the light modulation element and a lighting time of the light source by changing a voltage applied to each light modulation element according to gradation information. This is a method of driving the optical modulator.

Furthermore, an optical modulation element in which a photoconductive layer and an optical modulation element are arranged between a pair of electrodes to which a voltage is applied, and a signal light source for providing the photoconductive layer with optical information including gradation information,
In a method of driving an image display device having a read light source for giving read light for reading image information to the optical modulation element, a lighting time of the read light source is controlled so that the optical modulation element has a predetermined optical state. The driving method is characterized in that the overlapping time of the present time and the lighting time is modulated according to the gradation information.

The present invention also provides a method for driving an optical modulator having a light source and a light modulating means containing an optical modulator,
The voltage applied to the optical modulation element changes with time according to the gradation information, thereby modulating the timing at which the optical modulation element transits from the first alignment state to the second alignment state,
A method of driving an optical modulation device, characterized in that duty-modulated optical information is obtained according to the gradation information by turning on the light source.

Further, the present invention provides a method of driving an optical modulator having a light source, an optical modulation element exhibiting a bistable state, and a modulation means containing a photoelectric conversion material, wherein the optical modulation element and the photoelectric conversion material are provided. A voltage is applied to a pair of electrodes interposed between the electrodes to irradiate the photoelectric conversion material with optical information including gradation information, and the voltage applied to the optical modulation element changes with time according to the gradation information. By modulating the optical modulation element from the first stable state to the second stable state until the optical modulation element transits from the second stable state to the first stable state. A method of driving an optical modulator, wherein a maximum value of the modulated time is set shorter than a predetermined period so that a change in gradation level can be recognized.

Further, according to the present invention, in a method of driving an optical modulator having a light source and an optical modulator including an optical modulator and a photoelectric converter, the optical modulator and the photoelectric converter are interposed between the optical modulator and the optical modulator. By applying a voltage to the pair of electrodes, irradiating the photoelectric conversion substance with light information including gradation information, and changing the voltage applied to the optical modulation element with time according to the gradation information, It is possible to modulate the timing at which the optical modulation element transits from the first alignment state to the second alignment state, and set the maximum value of the lighting time of the light source to be shorter than a predetermined period so that the change of the gradation level can be recognized. It is a driving method of a characteristic optical modulator.

The present invention also provides a method of driving an optical modulation device having a light source and a light modulation means including an optical modulation element and a photoelectric conversion material, wherein the optical modulation element and the photoelectric conversion material are interposed between them. A voltage having polarity inversion and a DC component of substantially zero is repeatedly applied to the pair of electrodes within a predetermined period, and the photoelectric conversion substance is irradiated with optical information including gradation information,
By changing the voltage applied to the optical modulation element according to the gradation information with time, the timing at which the optical modulation element transits from the first alignment state to the second alignment state is modulated, and the predetermined period is maintained. In either the first half or the second half of
A method of driving an optical modulation device, characterized in that the light source is turned on.

The present invention further relates to an optical modulation element having a photoconductive layer and an optical modulation element arranged between a pair of electrodes to which a voltage is applied, and a signal light source for providing the photoconductive layer with optical information including gradation information. And a read-out light source for giving read-out light for reading out image information to the optical modulation element, in a driving method of an image display device, the read-out light source is turned on during a period different from a period during which the optical information is given. The driving method is characterized by controlling the time and modulating the overlapping time of the lighting time and the time when the optical modulation element exhibits a predetermined optical state according to the gradation information.

(Operation) According to the present invention, the timing at which the voltage applied to the optical modulation element exceeds the threshold value for transitioning the optical state of the optical modulation element changes in an analog manner depending on the gradation information. To do. As a result, the ON time of the optical modulator, that is, the time when the optical shutter is opened or the time when the mirror is displaced in a predetermined direction and the overlapping time of the lighting time of the light source are changed in an analog manner. Alternatively, the time integrated value of the reflected light amount corresponds to the gradation information. Therefore, the number of gradations is not limited to a digital amount such as a clock frequency, and A / D conversion of gradation information is not essential.

In addition, even if a digital (binary) display element having a sharp applied voltage and transmittance characteristic is used, analog modulation can be performed, which is an effect not heretofore considered.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described.

First, the basic modulation method of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an embodiment for realizing the modulation system of the present invention, in which 1 is an optical shutter for controlling the transmission of light as a light modulating means, 2 is a light source for generating light, DR1 is a driving means for driving the optical shutter, D
R2 is a drive means for turning on the light source, and CONT is a control means for controlling power supply and operation timing to the two drive means.

FIG. 2 is a graph showing an example of the characteristics of the optical modulation element (substance) of the optical shutter 1. For example, when the pulse width is constant and the applied voltage exceeds the threshold value V _th , the transmittance sharply increases. However, the transmittance becomes constant at the saturation value V _sat or more. If the optical modulator has a memory property, the optical state is kept constant even when the applied voltage is released.

FIG. 3 is a timing chart for explaining the basic operation of FIG. 1. 10 is an optical transition of the optical shutter, 20 is a light source lighting timing, and 30 is a signal applied to the optical shutter. . The applied signal 30 is a signal in which the amplitude (peak value) V _op and the pulse width PW _op further change according to the gradation information.

The light source emits light for a period t from turning on (ON) at time t ₁ to turning off (OFF) at time t ₃ . This period t is a predetermined time so that halftones can be recognized. When a signal modulated according to this timing is applied and the time integration of the applied voltage applied to the optical modulation substance exceeds a threshold value, the optical shutter transits from the dark state (Min) to the bright state (Max).

The rising timing t ₂ of this transition depends on the amplitude V _op and the pulse width PW _op . Since the amplitude V _op is modulated by the gradation information, the timing t ₂ eventually changes within the range of the time width TM according to the gradation information. t _off is the application timing of the signal for turning _off the optical shutter, and the time integration of the amount of light passing through the optical shutter 1 is the overlapping time of the lighting time and the time when the optical shutter is in the ON state. It will change accordingly. Therefore, if the pulse width PW _op is fixed and the amount of the amplitude V _op is changed in an analog manner, the time integration of the transmitted light amount can be easily modulated.

All conventional digital duty modulations
With the pulse width PW _op and the amplitude V _op of the applied signal 30 being constant, the application timing tt _on of the signal 30 is digitally changed according to the clock.

On the other hand, the present invention is novel in that the signal 30 is treated as an analog amount, which enables analog duty modulation.

FIG. 4 shows an example of a circuit for generating the analog signal 30. The inputted gradation information is transferred to the transistor Tr.
The signal having the modulated amplitude and the predetermined pulse width required for driving the optical shutter can be obtained by amplifying the signal by the amplifier 1 and sampling by the switch including the transistor Tr2.

Next, another basic modulation method of the present invention will be described with reference to FIG.

FIG. 5 shows an apparatus according to another embodiment of the present invention.

The point different from the system of FIG. 1 described above is that the optical modulating means is the light reflecting means 1A. A liquid crystal element or a mirror element is used as the light reflecting means.
In the case of a liquid crystal element, one of a pair of substrates enclosing liquid crystal is used as a transparent body and the other is used as a reflector, and light absorption or light reflection is selectively performed according to the alignment state of the liquid crystal. In the case of a mirror element, the angle of the reflecting surface of the mirror is controlled by changing the mirror, and it is selected whether the reflecting surface faces a predetermined direction or another direction.

Then, the overlapping time of the lighting time of the light source and the on time of the reflecting means is analog-modulated according to the gradation data.

Here, the on-time of the reflection means is the time when the liquid crystal element is in the light-reflecting state or the time when the reflection surface of the mirror element faces a predetermined direction. Of course, as the on-time, the time in the light blocking state can be treated as the on-time, and at this time, the optical state is only reversed.

(Drive Circuit) The drive circuit used in the present invention will be described.

FIG. 6 is a diagram showing a drive circuit of the optical modulation means used in the present invention. Here, the optical modulation means is C
Shown by _LC .

Assuming that the value of the resistance R _PC changes depending on the gradation information, first, a sufficient voltage exceeding the threshold value of the optical modulation means C _LC is applied. If the value of R _PC is high at this time, C
_The time when the voltage applied to _LC exceeds the threshold is delayed. On the other hand, if the value of R _PC is low, the time at which the voltage applied to C _LC exceeds the threshold value becomes earlier. Therefore, with these times,
By adjusting the lighting timing and lighting time of the light source, analog duty modulation of transmitted light or reflected light becomes possible.

FIG. 7 is a diagram showing another drive circuit. Figure 6
Differs in that connected in parallel to the optical modulation means C _LC resistor R _PC, with capacitive C _PC. In this case, a drive voltage Vd sufficient to exceed the threshold is applied for a predetermined time and _CLC
Is turned on, discharge development based on the time constant of the RC circuit is used. Time the voltage applied to C _LC is lower than the threshold and the value of the resistance R _PC is if slow discharge high slower.

On the other hand, the higher the value of R _PC, the faster the discharge and the earlier the time when the voltage applied to C _LC becomes lower than the threshold value. If this time is set within the lighting time of the light source, the light transmission or reflection time is subjected to analog duty modulation due to the difference in timing.

FIG. 8 shows an example of yet another drive circuit. The value indicated by the variable voltage V _v is gradation information. The difference from FIG. 7 is that the time constants of the RC circuits R _PC and C _PC are fixed.
_The timing at which the voltage applied to _LC becomes equal to or lower than the threshold value is determined by the voltage V _v which is gradation information. Accordingly, analog duty modulation can be performed by adjusting the timing with the lighting time in the same manner as in FIG.

(Light Source) The light source used in the present invention will be described. The light generated by this light source is selected from natural sunlight, white light, monochromatic light such as red (R), green (G), and blue (B), and a combination thereof, as required.
Therefore, examples of the light source used in the present invention include a laser light source, a fluorescent lamp, a xenon lamp, a halogen lamp, a light emitting diode, and an electroluminescent element. ON / OFF of these lightings is controlled by the light source driving means according to the driving timing of the optical modulation means.
In particular, it is desired that the continuous lighting time of the reading light source be at most the reciprocal (1/60 second) of the flicker frequency (for example, 60 Hz) at which humans can recognize the flicker. In the case of color display, it is desirable to turn on the R, G, and B light sources at different timings, and to perform optical modulation of R, G, and B in a time-division manner. Further, the color (wavelength range) of the irradiation light may be changed by changing the color of the color filter by time division using a white light source and a color filter.

(Optical Modulating Element) The light modulating means used in the present invention is a transmission type element called an optical shutter (light valve) for modulating the light transmittance or a light reflecting means for modulating the light reflectance. A reflective element may be used. A typical example of these is called a spatial light modulator (SLM).

The optical shutter used in the present invention may be one that can exhibit two optically different states.

Preferably, liquid crystal is used as the optical modulation substance.

As the optical modulation element using liquid crystal, it is desirable to arrange liquid crystal between a pair of electrodes so that liquid crystal molecules change their alignment state according to an applied electric field. Then, the light transmittance is controlled through the polarizing element according to the optical characteristics of the molecular orientation.

Specifically, it is preferable to use a liquid crystal cell in which liquid crystal is sealed between a pair of substrates. A transparent electrode or an alignment film is provided on at least one surface of the pair of substrates as needed.

As the substrate, translucent glass, plastic, quartz or the like is used. When the element is used as the reflection means, a non-translucent substrate can be used as one of the substrates.

As the transparent electrode, a metal oxide conductor such as tin oxide, indium oxide, or ITO is preferably used.

As the alignment film, a polymer film subjected to uniaxial alignment treatment such as rubbing or an inorganic film formed by oblique vapor deposition is preferable.

As the liquid crystal, a nematic liquid crystal exhibiting a nematic phase when operating as a cell, or a smectic liquid crystal exhibiting a smectic phase when operating as a cell is preferably used. More preferably, a liquid crystal having a memory property is desirable, and specific examples thereof include a chiral smectic liquid crystal and a chiral nematic liquid crystal.

The reflecting element used in the present invention is a DMD (Digital Micromirror) in which the reflecting surface of a metal film reflector is moved by an electrostatic force by an applied voltage and the angle of the reflecting surface is changed to modulate the outgoing direction of reflected light.
Examples of the device include a device referred to as a device, and a liquid crystal device that reflects light when the liquid crystal is oriented in a transmissive state by using one surface of the liquid crystal cell as a reflector and the other surface as a transmissive body.

FIG. 9 is a graph showing the applied voltage transmittance characteristics of the optical modulation element (substance) used in the present invention. D
In the case of MD, it can be regarded as a graph showing the applied voltage dependence of the amount of reflected light reflected in a predetermined direction.

(A) has a state transition with a positive threshold value as a boundary value, (b) has positive and negative threshold values and further has hysteresis, and (c) shows a hysteresis. Positive and negative thresholds are caused by.
(D) has a voltage of 0 as a threshold value. This figure 9
Shows an ideal characteristic for simplification of description, and actually has a slight inclination between the threshold value and the saturation value as shown in FIG.

Consider matching with a drive circuit. 9 (a) and 9 (b) are preferably combined with the parallel circuit shown in FIGS. 7 and 8, and FIGS. 9 (c) and 9 (d) are combined with the series circuit shown in FIG. Good.

Here, the structure of the spatial light modulator as a reflecting element that is preferably used in the present invention will be described with reference to FIG.

Reference numerals 511 and 516 denote transparent substrates 512 and 51.
Reference numeral 5 is a transparent electrode, 513 is a photoelectric conversion substance, 514 is a dielectric, and is a multilayer film in which a number of thin films are laminated. 517
Is an optical modulator. The photoelectric conversion substance may be a single layer or a plurality of layers of a photoconductive material, a PN junction or a PIN.
It may be a photovoltaic layer having a junction.

A non-single crystal semiconductor material is preferably used as the photoelectric conversion material described above. Specifically, it is amorphous silicon, amorphous silicon germanium, amorphous silicon carbide, microcrystalline silicon, microcrystalline silicon germanium, microcrystalline silicon carbide, or the like.

Further, nitrogen, oxygen, boron, phosphorus, hydrogen, fluorine, chlorine or the like may be contained in order to adjust the resistivity as required.

The above-mentioned liquid crystal is preferably used as the optical modulator. Specifically, examples of the chiral smectic liquid crystal include ferroelectric liquid crystal having a memory property described in US Pat. No. 5,120,466 and US Pat. No. 5,189,536. .

Examples of chiral nematic (cholesteric) liquid crystals include liquid crystals having a memory property and exhibiting a stable state of 2, which are described in US Pat. No. 4,239,345 and European Patent Publication No. 0569029A2. To be

As the multi-layer film, it is preferable to use a stack of several to several tens layers of dielectric materials having different refractive indexes such as titanium oxide and silicon oxide.

When the above-mentioned spatial light modulator, particularly an optical modulator having a memory property is used, a minute region (domain) in the plane of the photoelectric conversion substance according to the inputted optical information.
The amount of charge generated differs for each.

Therefore, in the minute regions of the optical modulation substance corresponding to the minute regions of the photoelectric conversion substance, the optical states transit at the timings corresponding to the optical information. In this way, the time integral of the amount of light transmitted or blocked through the minute region is modulated.

Therefore, in the above spatial light modulator,
Since analog halftone display can be performed for each minute area, super-high-definition, multi-tone monocolor or full-color display can be performed.

(A) has a state transition with a positive threshold voltage as a boundary value, (b) has positive and negative thresholds and further has hysteresis, respectively.
(C) has a positive and negative threshold value due to hysteresis. (D) has a voltage of 0 as a threshold value. FIG. 9 shows ideal characteristics in order to simplify the description, and actually has a slight slope between the threshold value and the saturation value as shown in FIG.

Consider matching with a drive circuit. 9 (a) and 9 (b) are preferably combined with the parallel circuit shown in FIGS. 7 and 8, and FIGS. 9 (c) and 9 (d) are combined with the series circuit shown in FIG. Good.

[0078]

【Example】

(Embodiment 1) FIG. 10 is a schematic diagram for explaining a method of driving an optical modulator. Reference numeral 101 is a liquid crystal element in which a ferroelectric chiral smectic liquid crystal is arranged between transparent substrates having a pair of electrodes, 103 is a gradation information generating circuit for generating gradation information, 104 is a light source, and 105 is an observer. The driver circuit is a circuit including the capacitor C _pc and the transistor 102, and the voltage applied to the liquid crystal is changed by changing the resistance between the source and the drain (or the emitter and the collector) depending on the potential of the gate or the base of the transistor. The timing at which the liquid crystal inversion threshold is exceeded changes. Vext is a voltage applying means for applying a voltage for resetting the liquid crystal element and a voltage for driving the liquid crystal element. Cf1c represents the capacitance of the liquid crystal.

The gradation information generating circuit 103 includes a light emitting diode PED and four variable resistors VRB, VRG, VRR and VR.
W and four transistors TB, TG,
TR, TW and power supply VCC. The diode PED and the transistor 102 constitute a photocoupler.

An electric signal as gradation information of each color given as a variable resistance value becomes light information by the light emitting diode PED.

The light source 104 includes light emitting diodes EDR, EDG, EDB for generating light of three colors of RGB. BR
Is a variable resistor for white balance provided as needed.

FIG. 11 is a drive timing chart of FIG. 10, in which 103T shows output timing of optical information,
Vflc represents the voltage applied to the liquid crystal, Tran represents the transmittance of the liquid crystal element, 104 represents the lighting timing of the light source, and 105T represents the amount of transmitted light recognized by the observer.

First, white light for resetting is applied and at the same time, a reset pulse is applied by the voltage applying means Vext. Thus, the liquid crystal is once oriented to a dark state.

Next, light is output according to the R gradation information, and at the same time, the R light emitting diode EDR is turned on, and Ve
xt applies a voltage of the opposite polarity to the electrode of the liquid crystal element. Since the amount of R light is extremely small during this period, the effective voltage applied to the liquid crystal does not exceed the threshold value V _th , so that the liquid crystal element does not pass R light.

After that, white light is given again and V
ext increases, and the liquid crystal is inverted to a light transmitting state. However, at this time, since the light source is not turned on, the observer sees the dark state continuously.

Although Vext becomes a negative voltage, the effective voltage applied to the liquid crystal does not exceed the threshold value, so that the liquid crystal element remains in the bright state. However, the light source is not turned on during this period.

In this way, the R display period ends.

Next is a G display period in which the same driving as the R display period is performed. Here, since the light amount of the G information is larger than the case of R, the voltage applied to the liquid crystal exceeds the threshold value at time trv. Then, the time toff at which the lighting of the light source ends
Since the liquid crystal element transmits the G light for the period up to, the observer recognizes the intermediate level G light.

At the same time, the next is the B display period in which the same driving as the R and G display periods is performed. Here, since the light amount of the B information is larger than the case of G, the voltage applied to the liquid crystal exceeds the threshold value at time trv2. Then, since the liquid crystal element transmits the B light during the period until the time toff2 at which the lighting of the light source ends, the observer recognizes the intermediate level B light closest to the maximum bright state. Since the duty of the lighting time of the light source 104 of each color is one half or less of the cycle of each color and one sixth or less of the cycle of all colors, the maximum duty of the overlapping time is also half of the cycle of each color. It is 1 or less, or 1/6 or less of the cycle of all colors.

As described above, in this embodiment, the timing when Vflc exceeds the threshold value is changed according to the gradation information. Then, when the gradation information corresponding to the minimum level transmission state is input, the transmission period (on period) of the liquid crystal element and the lighting period of the light source do not overlap with each other when the light source is on. , Set the light-off time. Specifically, here, the display period of each color may be set to 30 microseconds, and the continuous lighting time of the light source may be set to be shorter than 15 microseconds.

Thus, in this embodiment, a desired intermediate state can be obtained from the range from the minimum brightness level to the maximum brightness level. Further, since the voltage applied to the liquid crystal becomes positive and negative symmetrical with respect to the reference potential, D applied to the liquid crystal
The C component becomes substantially 0, and deterioration of the liquid crystal element can be suppressed.

(Embodiment 2) FIG. 12 is a schematic diagram for explaining a method of driving an optical modulator. 201 is a reflective liquid crystal element in which liquid crystal is arranged between substrates having a pair of electrodes,
204 is a light source driving circuit for driving the light source, C _pc is a capacitance element, R _pc is a resistance element, and Vd is a driving voltage source. This system is a circuit in which the resistance value changes when gradation information is input to the resistance element _Rpc .

The characteristics of the liquid crystal used are as shown in FIG.

FIG. 13 is a driving timing chart of FIG. 12, where Vs1 is the application timing of the power source Vd
1c indicates a voltage applied to the liquid crystal, Tran indicates the reflectance of the liquid crystal element, 204 indicates the lighting timing of the light source, and 205 indicates the amount of transmitted light recognized by the observer. 1 indicates a case where the value of R _pc is low, m indicates a case where the value of R _pc is an intermediate level, and n indicates a case where the value of R _pc is high, which correspond to analog gradation information.

First, when Vd is applied to the liquid crystal element at time ton, the voltage V1c applied to the liquid crystal becomes a voltage V1 that sufficiently exceeds the threshold value. At the same time, the liquid crystal element has a maximum reflectance.

Since the voltage Vd is released at the time toff, the voltage V1c applied to the liquid crystal gradually decreases according to the resistance value R _pc , and falls below the threshold value at a certain timing. Since this timing depends on the gradation information, in the case of 1, the time t
_The reflectance T ran becomes minimum at time t _x2 in the case of _x1 and m, and at time t _x3 in the case of n. Since the light source is set to start lighting at time t _x1 and turn off at time t _x3 , the reflected light amount corresponding to 1, m, and n is 205T. By setting the lighting time in this way, the linearity of the halftone display becomes excellent.

As described above, in this embodiment, the timing when V1c falls below the threshold value is changed according to the gradation information.
When the gradation information corresponding to the minimum level reflection state is input during the period when the light source is on, the reflection period (on period) of the liquid crystal element and the light source on period do not overlap. , Set the lighting time of the light source.

As described above, in this embodiment, a desired intermediate reflection state can be obtained from the range from the minimum brightness level 1 to the maximum brightness level n.

(Embodiment 3) FIG. 14 is a schematic diagram for explaining a method of driving an optical modulator. 301 is a reflective liquid crystal element in which liquid crystal is arranged between substrates having a pair of electrodes,
Reference numeral 304 denotes a light source drive circuit that drives a light source, C _pc is a capacitive element, R _pc is a resistive element, Vv is a drive voltage source, and V _so is a switch for turning on / off the supply of a voltage signal from the drive voltage source Vv. In this system, a supply voltage signal from a drive voltage source is analog gradation information.

The characteristics of the liquid crystal used are as shown in FIG.

FIG. 15 is a timing chart of the driving shown in FIG. 14, where Vso is the application timing of the gradation signal and Vso is
1c is the voltage applied to the liquid crystal, Tran is the reflectance of the liquid crystal element, 304 is the lighting timing of the light source, and 305 is the amount of transmitted light recognized by the observer. 1 indicates a case where the voltage value V1 of the gradation signal is low, m indicates a case where the voltage value Vm of the gradation signal is an intermediate level, and n indicates a case where the voltage value Vn of the gradation signal is high.

First, when Vv is applied to the liquid crystal element at time ton, the voltage V1c applied to the liquid crystal becomes voltages V1, Vm and Vn that sufficiently exceed the threshold value. At the same time, the liquid crystal element has a maximum reflectance.

Since the voltage Vv is released at the time toff, the voltage V1c applied to the liquid crystal gradually decreases according to the voltage Vv3, and falls below the threshold value at a certain timing. Since this timing depends on the gradation information, in the case of 1, the time t
_In the case of _x1 , m, at time t _x2 , and in the case of n, at time t _x3 , the reflectance Tran of the liquid crystal element transits to the minimum state. Here, the light source starts to turn on at time t _x1 and then goes to time t _x3.
Since it is set to be turned off at, the reflected light amount corresponding to 1, m, and n is as indicated by 305T.

As described above, in this embodiment, the timing when V1c falls below the threshold value is changed according to the gradation information.
Then, when the gradation information corresponding to the minimum level of the reflection state is input, the reflection period (on period) of the liquid crystal element and the light emission period of the light source do not overlap each other when the light source is lit. , The lighting time of the light source is set.

In this way, in this embodiment, a desired intermediate reflection state can be obtained from the range from the minimum brightness level 1 to the maximum brightness level n.

(Embodiment 4) FIG. 16 is a schematic diagram for explaining a method of driving an optical modulator. 401 is a reflective liquid crystal element in which an antiferroelectric chiral smectic liquid crystal is arranged between substrates having a pair of electrodes, 404 is a light source driving circuit for driving a light source, C _pc is a capacitive element, R _pc is a resistive element,
Vv is a drive voltage source, and Vso is a switch for turning on / off the supply of the voltage signal from the drive voltage source Vv. In this system, a supply voltage signal from a drive voltage source is analog gradation information. Reference numeral 405 represents an observer.

The characteristics of the chiral smectic liquid crystal used are as shown in FIG. 9 (a).

FIG. 17 is a timing chart of the driving shown in FIG. 16, where Vso is the application timing of the gradation signal and Vso is
af1c indicates the voltage applied to the liquid crystal, Tran indicates the reflectance of the liquid crystal element, 404 indicates the lighting timing of the light source, and 405 indicates the amount of transmitted light recognized by the observer. 1 indicates a case where the voltage value of the gradation signal is low, m indicates a case where the voltage value of the gradation signal is an intermediate level, and n indicates a case where the voltage value of the gradation signal is high.

First, when Vv is applied to the liquid crystal element at time ton, the voltage Vaf1c applied to the liquid crystal becomes voltages V1, Vm and Vn that sufficiently exceed the threshold value. At the same time, the liquid crystal element has a maximum reflectance.

Since the voltage Vv is released at the time toff, the voltage Vaf1c applied to the liquid crystal gradually decreases according to the voltage Vv, and falls below the threshold value at a certain timing. Since this timing depends on the gradation information, in the case of 1, the time is t _x1.
Then, the reflectance Tran of the liquid crystal element makes a minimum transition at time t _x2 in the case of m and at time t _x3 in the case of n. Here, since the light source is set to start lighting at time t _x1 and turn off at time t _x3 , the reflected light amounts corresponding to 1, m, and n are as shown at 405T.

It is more preferable that one cycle (Prd1, Prd2) is 1/30 second or less and the continuous lighting time of the light source is 1/60 second or less at the longest.

The present embodiment differs from the embodiments shown in FIGS. 14 and 15 in that the period Pr is used because the antiferroelectric liquid crystal is used.
At d2, the voltage Vv having the polarity opposite to that of the previous period Prd1 is applied. Since the antiferroelectric liquid crystal is used, there are two thresholds V _th 1 and V _th 2 due to hysteresis, and even if the polarity of the voltage Vv is reversed, the alignment state of the liquid crystal is the same as shown by Tran. . The chiral smectic liquid crystal is suitable as the liquid crystal used in the present invention because it has a high transition speed (switching speed) between two molecular orientation states.

As described above, in the present embodiment, Vaf1c
The timing at which is below the threshold is changed according to the gradation information. Then, when the gradation information corresponding to the minimum level of the reflection state is input, the reflection period (on period) of the liquid crystal element and the light emission period of the light source do not overlap each other when the light source is lit. , The lighting time of the light source is set.

The present invention adopts the optical modulation means in each of the above-mentioned examples, that is, the optical shutter and the light reflection means, in which a large number of optical modulation elements are two-dimensionally arranged or the elements are arranged continuously. .

Specifically, it is a panel in which a large number of pixels are arranged in a matrix or a DMD in which a large number of micromirrors are arranged in a matrix. The element disclosed in JP-A-59-216126 can be used as the continuous pixels. This element is a photo-writing type element in which electrodes are not patterned for each pixel, and is an element capable of handling a two-dimensional image.

Next, a method of driving the image display device as the optical light modulator according to the present invention will be described.

FIG. 18 is a sectional view of an optical modulator for an image display device according to an embodiment of the present invention.

FIG. 19 is a diagram showing the molecular orientation of the chiral smectic liquid crystal used in the device.

FIG. 20 is a diagram showing the electro-optical characteristic of the liquid crystal molecule.

FIG. 21 is a timing chart showing the operation.

The element shown in FIG. 18 is a so-called reflection type liquid crystal panel, in which a transparent electrode 512 is formed on a transparent substrate 511, a photoconductive layer 513 as a photosensitive layer is provided thereon, and a reflection layer is formed on the transparent electrode 512. A dielectric multilayer film 514 is provided as a layer. The transparent electrode 5 is formed on the other transparent substrate 516.
15 are provided. A chiral smectic liquid crystal 517 as an optical modulator is disposed between these two substrates. 522 is a polarizing element. Although not shown, an alignment film for aligning liquid crystal molecules is provided at the liquid crystal interface between the electrode 515 and the reflective layer 514. Vext is electrode 5
Voltage applying means for applying voltage to 12, 515;
1 is reset light, 518 is writing light including gradation information,
Reference numeral 519 denotes read light for reading the modulated gradation information, that is, an image.

The equivalent circuit of this element is the same as that shown in FIG.

FIG. 19A shows the liquid crystal molecules MOL in the first alignment state, and B shows the second alignment state. When a voltage + Vu is applied to the liquid crystal in the first alignment state A, the liquid crystal transitions to the second alignment state. Thereafter, the liquid crystal remains in state B even when the voltage is set to 0, that is, when there is no electric field. Next, when a voltage -Vu is applied, the liquid crystal transits to state A and maintains state A even when the electric field is released. Such a transition is called liquid crystal inversion or switching. Since each state A and B is a stable state, this liquid crystal has a memory property.

Since these states A and B are optically different from each other, if they are appropriately combined with a polarizing element, one state has the maximum light transmittance and the other has the minimum light transmittance. be able to. Here, Vu is set assuming that the saturation value of the applied voltage is substantially the same as the inversion threshold value of the liquid crystal.

The operation of this element will be described. To illustrate the nature of the operation, the capacitance C _pc equal volume capacity Cf1c and the photoconductive layer of the liquid crystal layer, the resistance component of the liquid crystal layer is infinite, the impedance of the reflective layer to 0. 5 in FIG.
21T is 5 of reset light applied to the photoconductive layer 513.
18T indicates the irradiation timing of the writing light which is irradiated on the photoconductive layer 513 and whose intensity changes according to the gradation information. Ve
xt represents an AC voltage applied between the transparent electrodes 512 and 515 at both ends of the element, and Vflc represents an effective voltage applied as a divided voltage across the liquid crystal layer 517. + Vu and -Vu are voltages at which the liquid crystal is inverted from the first to the second or from the second to the first alignment state as shown in FIG. Tran represents the alignment state of FLC, but here, it is composed of a polarizer analyzer so that the first alignment state is a dark state where the transmittance is minimum and the second alignment state is a bright state where the transmittance is maximum. It is assumed that the positional relationship of the polarizing elements is set. 504T is the liquid crystal layer 51
505T of the read irradiation light for irradiating 7 is extraction light that is extracted by being reflected by the reflective layer via the liquid crystal, the polarizer, and the analyzer.

First, the period from t ₅₀ to t ₅₁ is the reset period. Potential -V ₁ is applied as Vext, the reset light is irradiated to the photoconductive layer. The reset light generates photocarriers (electron-hole pairs) in the photoconductive layer, and the electron-holes are separated by the electric field applied to the photoconductive layer and run in the opposite direction, sandwiching the liquid crystal layer 517. To face each other. Vflc approaches the potential -V ₁ by this behavior. Explaining with the equivalent circuit of FIG. 6, the resistance component in the photoconductive layer is reduced by the photoconductive effect, self-discharge occurs, and the potential applied to the photoconductive layer by the divided voltage is reduced.
It may be considered that c approaches −V ₁ . If the reset light has sufficient light intensity, regardless of the previous state, t
_By the time point ₅₁ , Vflc is reset like -V ₁ and the liquid crystal is secured in the first alignment state (dark). At t _{51, the} reset light is turned off and Vext is set to + V ₂ . Then Vf
The potential of lc is V ₃ = V ₁ + by the 1: 1 capacitance division.
The potential changes to (V ₂ − (− V ₁ )) / 2. If the writing light is not irradiated as in the first cycle, Vf up to t ₅₂
lc remains V _3, the liquid crystal which is still the first orientation state (dark) because it is V ₃ <Vu. V after t ₅₂
The polarity of ext is reversed and the same operation from t ₅₀ to t ₅₂ is performed again. As a result, Vflc becomes 0 when integrated within one cycle, that is, the DC component becomes 0, and AC symmetry of the driving waveform required for stable FLC driving is guaranteed. t
_{From 52} to t ₅₃ , Vflc exceeds Vu and is reset to + V ₁ , and the liquid crystal enters the second alignment state (bright).

Now, in the second cycle, writing light is emitted. This writing light is not as strong as the reset light, but is slower than the time constant, but Vflc approaches Vext. When the writing light intensity is high to some extent, Vflc exceeds Vu at T = t _x1 between t ₅₁ and t ₅₂ , and the liquid crystal inverts from the first alignment state to the second alignment state at this point. When the writing light becomes stronger as in the third period, t _x1 approaches t ₅₁ , and the second alignment state is started at an early time. In both the second and third cycles, the same writing light as that applied during the period from t ₅₁ to t ₅₂ is applied during the period from t ₅₃ to t ₅₄ (t _{50 of the} next period), so that Vflc is −Vu at t _x2.
, The liquid crystal returns to the first alignment state (dark). The AC symmetry of Vflc is secured in both the first and second third cycles, and the liquid crystal has a first alignment state and a second alignment state of 50% each in each cycle. The phase of the second alignment state of the FLC shifts forward as the writing light intensity increases. For such liquid crystal operation, t in each cycle
_{When the} reading light is irradiated during the period from ₅₁ to t _52, the observer
Irradiation time of readout light and second alignment state of FLC (bright)
You will observe the light only for the overlapping time. Although light cannot be extracted in the first cycle, as the writing light intensity increases, the overlapping time also increases as in the second and third cycles, and the number of extracted light beams also increases. If each period is a time equal to or lower than the flicker frequency of the human eye (for example, 1/60 second), the observer's eye will observe it as a change in light intensity.

Also, not between t ₅₁ and t ₅₂ , but between t ₅₃ and t _54.
If the reading ratio is applied during the period, the overlapping time decreases and the number of extracted light fluxes decreases as the writing light intensity increases. That is, negative / positive conversion can be performed by the writing light and the extraction light. Since the writing light spreads in a quadratic plane, an in-plane potential distribution can be created depending on the writing light intensity, and a so-called optical writing type spatial light modulator capable of two-dimensional optical writing and reading can be constructed. it can. Using this, a monochrome film viewer can be configured.

FIG. 22 is a system configuration diagram in which a full-color film viewer as an image display device is constructed by using the optical writing type spatial modulation element according to the present invention.

As the light source on the writing side, light emitting diodes (LEDs) of three colors of R, G, B are prepared for each color.

530R is an LED for writing light source of R, 5
Reference numeral 30G is a G writing light source LED, 530B is a B writing light source LED, 535 is a reset light source, 531 is a three-color mixing prism having an R reflecting surface and a B reflecting surface. 536 is a light modulation element, 532, 534 are lenses, 5
33 is a film and 537 is a prism. 539R is an LED for reading light source of R, 539G is LED for reading light source of G, 539B is LED for reading light source of B, 5
Reference numeral 38 is a three-color mixing prism having an R reflecting surface and a B reflecting surface.

A timing chart showing the operation is shown in FIG.

1 / (flicker frequency ×
3) = Set to about 5 ms or less, and set the writing light source to RGB1
The lights are turned on sequentially in cycles. RGB LEDs are also prepared for the light source on the reading side, and the same color as the writing side is sequentially turned on. The film 533 has video information, and here, gradation information having a transmittance of 0% for R, 50% for G, and 100% for B is included.

During the three cycles, the colors are color-mixed by the eyes, and the images are displayed in full color.

As described above, the film 533 can be either a positive film or a negative film simply by switching the lighting riming of the reading light source.

If a transmissive liquid crystal TV with a color filter is arranged in place of the film 533 and a brighter halogen lamp + color rotation filter is used as the reading light source,
It can be a video projector.

In the case of monochromatic writing, monochrome OH
In the case where the amount of light to be written in a specific pixel area does not change, such as when forming P, the reset light is not always necessary.

Further, when the reset light is used, it is sufficient that the intensity is equal to or higher than a certain intensity, so that there is no problem even if writing is superposed during the reset period.

Another embodiment of the present invention will be described below with reference to FIGS.

The optical system configuration of the image display device is shown in FIG.
2 is the same as that shown in FIG. 2, and the configuration of the optical modulator is shown in FIG.
8, the description is omitted.

(Embodiment 6) FIG. 24 is a timing chart showing a driving method of an image display device using the optical modulator according to the present embodiment.

The basic operation is the same as that of the embodiment shown in FIG. 21, but the difference is that the writing light is only in the first half of the writing period of each cycle, t _{61 to} t ₆₂ , as shown at 518T. It is to irradiate and turn it off during the other period (second half). Light emitted in the period t ₆₄ ~t ₆₅ does not contribute to readout. Then, during the period from t _{62 to} t ₆₃ which is the latter half of the writing period, uniform bias light is applied (505T). When the writing light including the gradation information is 0, the voltage applied to the liquid crystal is −V ₆ and t ₆₁ to
It is constant during the period of t ₆₂ . Next, when bias light is applied at time t ₆₂ , the voltage applied to the liquid crystal increases in the positive direction due to the lower resistance of the photoconductive layer. Here writing light minimum even if the time t ₆₃ of the liquid crystal in the case of threshold (+ V
In order not to exceed u), the value of R _pc or C _pc is set to match the timing of time t ₃ . Therefore, since the writing light is minimum, that is, 0 in the first period, the reading light is also minimum, that is, 0 (505T).

The period from t _{63 to} t _{60 of the} next cycle is the inversion operation. Therefore, during this period, since there is no irradiation for reading, the image information is not reproduced. Since the writing light is at the intermediate level in the second period, the resistance of the photoconductive layer decreases during the period from t _{61 to} t ₆₂ , and the liquid crystal is also applied with a voltage higher than −V _{6 in the} positive direction.

When the bias light is applied during the period t _{62 to} t ₆₃ , the read voltage is applied because the initial voltage value applied to the liquid crystal is higher than −V ₆ at the time t ₆₂ in the second cycle, unlike the first cycle. Time t in the middle of the period (t _{61 to} t ₆₃ )
Vflc exceeds the threshold value + Vu at _x1 . Therefore, T _x1
Since the liquid crystal has the maximum transmittance during the period from t ₆₃ to t ₆₃ (Tra
n), the reading light is reflected by the reflective layer of the element. Then, the period during which the reading light is reflected (t _{x1 to} t ₆₃ ).
Are modulated according to the writing light amount. t ₆₃ and later is the inversion operation.

The writing light is maximum in the third period (518T). Therefore, the voltage V applied to the liquid crystal at the first time t ₆₂ in the period (t _{62 to} t ₆₃ ) where the bias light is irradiated.
flc exceeds the threshold value + Vu. Therefore, the liquid crystal has the maximum transmittance during the whole period (t _{62 to} t ₆₃ ) where the reading light is irradiated. Therefore, the read light incident on the element is reflected in a predetermined direction, but the time integration of the reflected light amount becomes maximum.

As described above, the time for which the reading light is reflected is determined according to the light amount of the writing light. Therefore, if the writing light amount changes in an analog manner, the reflection time also changes in an analog manner.

The period t _{63 to} t ₆₀ is an inversion operation, and the polarity of the applied voltage Vext is inverted during this period, and the writing light bias light is irradiated with the same light amount again. This allows
Since the time integral per one cycle of the effective voltage applied to the liquid crystal is 0, deterioration of the liquid crystal can be suppressed.

In this embodiment, the amount of bias light is
It is appropriately determined in consideration of the time constant of the photoconductive layer and the length of the periods t _{60 to} t ₆₃ . The light source of the bias light may be the same as or different from the light source of the reset light. Preferably, both the light source for bias light and the light source for reset light have their own light control means so that the light amount can be set independently.

[0149] In the present embodiment, it can be displayed 1/30 second one cycle, a good halftone not observed flicker Setting up t ₆₀ ~t ₆₃ to about 1 second 60 minutes.

(Embodiment 7) This embodiment is the same as the embodiment 6 described above.
In the above, the read light source and the write light source are independently lit R, G, and B three-color light sources, and the first cycle is R
In the writing and reading periods of 2), the second period is assigned to the G writing and reading period, and the third period is assigned to the B writing and reading period, and image reproduction by full-color light modulation is performed.

(Embodiment 8) FIG. 25 is a timing chart showing a method of driving an image display device using the optical modulator according to this embodiment.

The basic operation is the same as that of the embodiment shown in FIG. The difference is that the voltage Vext applied to the element is changed over time instead of the operation of irradiating the bias light (t ₇₂
~ T ₇₃ ) This is the point where the operation is performed.

During the period t _{70 to} t ₇₁ , the reset light is irradiated (721T). At this time, Vext is 0.

At time t ₇₁ , Vext is set to the liquid crystal threshold voltage + Vu, but the writing light to the photoconductive layer is minimum (0).
Therefore, the voltage Vflc applied to the liquid crystal becomes + Vuu. If the capacity of the photoconductive layer is the same as the capacity of the liquid crystal, + Vuu is の of + Vu.

At time t ₇₂ , the writing light is set to 0,
The voltage Vext applied to the element is gradually increased from + Vu to + Vem.
Up with time. In response, the voltage Vflc applied to the liquid crystal also increases with Vext.

If + Vem is set to be twice as large as + Vu, Vflc exceeds the threshold value + Vu at time t.
It becomes ₇₃ . Thus, in the period t _{72 to} t ₇₃ , the reading light is turned on (704T), but since the alignment state of the liquid crystal does not transit, the liquid crystal does not reach the maximum transmittance.

The remaining period of t ₇₃ to t ₇₀ is the inversion operation. During this operation, the image is not reproduced because the reading light is not emitted.

The second cycle shows the case where the halftone writing light is irradiated (718T). Liquid crystal at time t ₇₀ is in the non-light-transmissive state by the reverse operation. V
With ext = 0, Vflc approaches voltage level 0.

At time t ₇₁ , Vext is the threshold value + Vu.
And the readout light starts to be turned on (704T). Ve
Although xfl increases Vflc, the threshold voltage + Vu
Does not reach

At time T ₇₂ , Vext begins to rise. Along with this, Vflc also rises, so that Vflc exceeds the threshold value + Vu at time t _x1 . Thus, the liquid crystal transitions to the alignment state exhibiting the maximum transmittance. Therefore, at this time _t72 , the lit readout light is reflected by the reflection layer through the liquid crystal layer, so that the image can be recognized. Then, the reflection times t _{x1 to} t _{73 of the} reading light are modulated according to the amount of writing light. t ₇₃ and later is the inversion operation.

The third period shows the case where the amount of writing light is maximum. The operation during the period from t _{70 to} t ₇₁ is the same in each cycle.

Vflc exceeds the threshold value + Vu at time t ₇₂ due to the amount of writing light irradiated at time t ₇₁ . Therefore, during the reading light lighting period t _{72 to} t ₇₃ , the liquid crystal transitions to the alignment state exhibiting the maximum transmittance. Therefore, the time during which the reading light is reflected by the element is maximum (705
T).

As described above, the time for which the reading light is reflected is determined according to the light amount of the writing light. Therefore, if the writing light amount changes in an analog manner, the reflection time also changes in an analog manner.

Further, the period t _{73 to} t ₇₀ is the inversion operation, the polarity of the applied voltage Vext is inverted during this period, and the writing light bias light is irradiated with the same light amount again. This allows
Since the time integral per one cycle of the effective voltage applied to the liquid crystal is 0, deterioration of the liquid crystal can be suppressed.

In this embodiment, the rate of change of Vext with time is appropriately determined in consideration of the time constant of the photoconductive layer and the length of the periods t _{71 to} t ₇₃ .

[0166] In the present embodiment, it can be displayed 1/30 second one cycle, a good halftone not observed flicker Setting up t ₆₀ ~t ₆₃ to about 1 second 60 minutes.

(Embodiment 9) This embodiment is the same as Embodiment 8 described above.
In the above, the read light source and the write light source are independently lit R, G, and B three-color light sources, and the first cycle is R
In the writing and reading periods of 2), the second period is assigned to the G writing and reading period, and the third period is assigned to the B writing and reading period, and image reproduction by full-color light modulation is performed.

(Embodiment 10) FIG. 26 is a timing chart for explaining a driving method of an image display device as an optical modulator according to another embodiment of the present invention.

To facilitate understanding of how the read light is duty-modulated in accordance with the optical signal containing the gradation information,
In each of the third to third cycles, the light quantity of the writing light is changed to three levels.

In the period t _{80 to} t ₈₁ of the first cycle, the reset light is applied to the photoelectric conversion layer of the device. At this time, since the reset pulse having the positive maximum peak value + Vm is applied between the pair of electrodes of the element, the voltage corresponding to the time constant of the element is applied to the liquid crystal.

At time t ₈₁ , the irradiation of the reset light is stopped and the application of the pulse having the maximum negative peak value −Vm as the first writing pulse is started between the pair of electrodes of the element. Period t _{81 to} t ₈₂ in which the first write pulse is applied
Is the first half of the writing period.

Since the first cycle shows the case where the writing light (818T) of the lowest gradation level is irradiated, the period t
₈₁ is a voltage applied to liquid crystal in ~t ₈₂ but not reach the -Vm, since exceed a negative threshold -Vu, the liquid crystal becomes oriented corresponding to OFF (Tran).

The period t _{82 to} t ₈₃ in which the second writing pulse is applied is the latter half of the writing period, but at this time, the writing light (818T) is not emitted. Instead, since the bias light (850T) that does not depend on the gradation information is applied to the photoelectric conversion layer, the voltage Vflc applied to the liquid crystal rises earlier than when there is no bias light. Voltage Vfl
When c exceeds the threshold value + Vu, the liquid crystal is turned on, and at time t _{83, the} reset voltage and the voltage V
Flc becomes a voltage -Vm, and an alignment state in which light is transmitted (or reflected) is set until the liquid crystal is turned off. The light source that emits the reading light (804T) starts lighting slightly earlier than time t ₈₂ , and continues lighting at least until time t ₈₃ .

Therefore, during the period t _{82 to} t ₈₃ , the overlap time (8
05T) is subjected to analog duty modulation according to gradation information. In this example, the read light (805T) modulated at the lowest gradation level of the write light (818T) is used.
Since the maximum gradation level of is obtained, the gradation levels of the writing light amount and the reading light amount are inverted.

In this example, optical information is written during the period t ₈₁ to t _{82 in} which the pulse with the maximum peak value (-Vm) is applied. During this period t _{81 to} t ₈₂ , a high voltage is applied to the element from the outside, so a high voltage is also applied to the photoelectric conversion layer. In this case, when light enters the photoelectric conversion layer, the voltage change applied to the liquid crystal is large. Become. Since the modulation voltage range is expanded in this way,
It is easy to increase the number of gradation levels.

Also in this example, as in the above-described several examples, the first half (t _{80 to} t ₈₃ ) which is the modulation period in each cycle and D
In the latter half of the C component canceling period (after t ₈₃ ), the voltage Vext applied to the element is inverted positively and negatively to make the DC component zero. Further, the reset light (821T), the bias light (850T), and the writing light (818T) are applied to the element in the latter half as in the first half. Each light emitted in the latter half is a dummy light that does not directly contribute to the modulation, but the voltage Vflc applied to the liquid crystal also plays a role of making the DC component substantially zero by making the voltage symmetric in the first half and the second half.

Of course, if the read light irradiation period in FIG. 26 is set to the latter half of each cycle, the first half (t _{80 to} t ₈₃ ) is a period for canceling the DC component, and the latter half (t _{83 and} thereafter) is the modulation period. Becomes

The light quantity of the reset light, the light quantity of the bias light, the applied voltage (Vext), etc. can be appropriately adjusted depending on the physical properties of the constituent material of the optical modulation element, the thickness of the liquid crystal or the photoelectric conversion layer, the element structure and the like. It should be set to.

Therefore, when simplifying the system,
It is preferable to increase the peak value of each pulse of the applied voltage Vext so that the normal operation is performed without the reset light and the bias light.

(Embodiment 11) FIG. 27 shows Embodiment 1 of the present invention.
3 is a timing chart for explaining a driving method of the optical modulator according to the first embodiment.

At the beginning of the first cycle, the photoelectric conversion substance is irradiated with the reset light (535), and a negative reset pulse from the outside is applied. In this way, the optical modulation substance is in a non-transmissive optical state.

Then, a positive write pulse Ve is externally applied.
Although xt is applied, the effective voltage applied to the optical modulator does not exceed the positive threshold because the light amount of optical information is at the lowest level. Therefore, no reading light is obtained even when the red light (539R) is turned on.

At the beginning of the second cycle, the reset pulse is applied as in the first cycle. Subsequently, since the photoelectric conversion substance is irradiated with the light information of the intermediate level of light together with the writing pulse, a large voltage is gradually applied to the optical modulation substance in the positive direction. At time t _x1 that exceeds the threshold value, the optical state transitions, and thus green light is read.

The third cycle is a cycle for reading blue light (539B). Since the photoelectric conversion substance is irradiated with the highest amount of light, the voltage applied to the optical modulation substance exceeds the threshold value immediately after resetting. Therefore, the highest level read light can be obtained.

In FIG. 27, the read light source (539
Although the lighting start of (R, 539G, 539B) is matched with the writing voltage application start time, this lighting start time may be during the reset period.

The time when the read light source of each color is turned off is preferably set to the time when the light source is irradiated with the write pulse and the information exceeds the threshold value at the latest. That is,
Assuming that the light amount indicated by 530GT in the second cycle of FIG. 27 is the minimum light amount that allows the voltage applied to the optical modulation substance to be equal to or higher than the threshold value in cooperation with the application of the write pulse, the light source (539G) The turn-off timing should be time t _x1 . However, if slight degradation of linearity is ignored, it may be slightly shifted from time t _x1 .

(Embodiment 12) FIG. 28 shows Embodiment 1 of the present invention.
6 is a timing chart for explaining a method of driving the optical modulator according to No. 2.

The point different from the example of FIG. 27 is that the light source of the corresponding color is continuously turned on during the entire period of each cycle, resetting and writing are performed in the first half of each cycle, and the second reset and dummy in the latter half. This is the point of writing.

By forcibly returning the optical state to the original state by resetting after writing, halftone optical information can be read even when the lighting duty of the light source in each cycle is 1.

The time to start the second reset should be set in the same manner as the light source turn-off timing defined in the example of FIG. Each cycle is 3 in both cases of FIG. 27 and FIG.
It is good to set it to 0 minutes and 1 second or less. Further, when handling monochrome information, the light source may be a single color light source.

[0191]

According to the present invention, good gradation display can be performed.

[Brief description of drawings]

FIG. 1 is a diagram of a basic driving device of an optical modulation element of the present invention.

FIG. 2 is a diagram showing the dependence of the transmittance of an optical modulation substance used in the present invention on the applied voltage (pulse width).

FIG. 3 is a diagram showing a timing chart for explaining another example of the basic driving method of the optical modulator of the present invention.

FIG. 4 is a diagram showing an example of a circuit for generating gradation information used in the present invention.

FIG. 5 is a diagram of another driving device of the optical modulation element of the present invention.

FIG. 6 is a diagram showing an example of a drive circuit for an optical modulator used in the present invention.

FIG. 7 is a diagram showing another example of a drive circuit for an optical modulation element used in the present invention.

FIG. 8 is a diagram showing yet another example of a drive circuit for an optical modulation element used in the present invention.

FIG. 9 is a diagram showing the applied voltage dependence of the transmittance of the optical modulator used in the present invention.

FIG. 10 is a diagram showing an optical modulator.

FIG. 11 is a diagram showing a drive timing chart of the optical modulator.

FIG. 12 is a diagram showing an optical modulator.

FIG. 13 is a diagram showing a drive timing chart of the optical modulator.

FIG. 14 is a diagram showing an optical modulator.

FIG. 15 is a diagram showing a drive timing chart of the optical modulator.

FIG. 16 is a diagram showing an optical modulator.

FIG. 17 is a diagram showing a drive timing chart of the optical modulator.

FIG. 18 is a cross-sectional view of an optical modulation element for an image display device used in the present invention.

19 is a diagram showing the molecular orientation of a chiral smectic liquid crystal used in the device of FIG.

20 is a diagram showing the electro-optical characteristics of the liquid crystal molecules of FIG.

FIG. 21 is a timing chart showing the operation of the device of FIG.

FIG. 22 is a diagram showing an image display device used in the present invention.

FIG. 23 is an operation timing chart of the image display device according to the example of the present invention.

FIG. 24 is an operation timing chart of the image display device according to another embodiment of the present invention.

FIG. 25 is an operation timing chart of the image display device according to another embodiment of the present invention.

FIG. 26 is an operation timing chart of the image display device according to another embodiment of the present invention.

FIG. 27 is an operation timing chart of the image display device according to another embodiment of the present invention.

FIG. 28 is an operation timing chart of the image display device according to another embodiment of the present invention.

Claims (56)

[Claims] 1. An optical modulator having a light source, a light modulating means, and means for driving the light modulating means, wherein the driving means applies to an optical modulating element of the light modulating means in accordance with gradation information. An optical modulation device, characterized in that it is means for modulating the overlap time of the ON time of the light modulation means and the lighting time of the light source by changing the applied voltage. 2. The optical modulator according to claim 1, wherein the means includes means for changing the voltage with time. 3. The optical modulation device according to claim 1, wherein said means includes means for applying a drive voltage to said light modulation means, and means for changing said drive voltage with time and applying it to said optical modulation element. . 4. The optical modulator according to claim 1, wherein the means includes a capacitive element and a resistive element. 5. The optical modulation device according to claim 1, wherein the optical modulation element is a liquid crystal exhibiting two optical states. 6. The optical modulation device according to claim 1, wherein the optical modulation element is a chiral smectic liquid crystal. 7. The optical modulation device according to claim 1, wherein the optical modulation element is a ferroelectric or antiferroelectric liquid crystal. 8. The optical modulation device according to claim 1, wherein the light source is a white light source. 9. The optical modulator according to claim 1, wherein the light source includes a red light source, a blue light source, and a green light source, and has lighting means for lighting these in different periods. 10. The optical modulator according to claim 1, wherein the gradation information is optical information. 11. A method of driving an optical modulator having a light source and a light modulator, wherein the voltage applied to the optical modulator element of the light modulator is changed according to gradation information, thereby the light modulator. A method for driving an optical modulation device, characterized in that an overlapping time between an ON time of the light source and a lighting time of the light source is modulated. 12. The method of driving an optical modulator according to claim 11, wherein the voltage is changed with time. 13. A method of driving an optical modulation device, comprising: a light source; a plurality of light modulation elements or a light modulation means including a planar optical modulation element; and a driving means for driving the light modulation means, The driving means modulates an overlap time between an ON time of the light modulation element and a lighting time of the light source by changing a voltage applied to each light modulation element according to gradation information. Driving method for optical modulator. 14. An optical modulation element in which a photoelectric conversion layer and an optical modulation element are arranged between a pair of electrodes to which a voltage is applied, and a signal light source for giving optical information including gradation information to the photoelectric conversion layer,
In a driving method of an optical modulation device having a read light source for giving read light for reading image information to the optical modulation element, a lighting time of the read light source is controlled so that the optical modulation element is brought into a predetermined optical state. A method for driving an optical modulation device, characterized in that the overlapping time of the presenting time and the lighting time is modulated according to gradation information. 15. A method of driving an optical modulator having a light source and an optical modulator including an optical modulator, wherein a voltage applied to the optical modulator changes with time according to gradation information, The optical modulation element modulates the timing of transition from the first optical state to the second optical state, and by turning on the light source, light information duty-modulated according to the gradation information is obtained. Driving method for optical modulator. 16. A method for driving an optical modulation device having a light source, an optical modulation element exhibiting a bistable state, and a light modulation means including a photoelectric conversion material, wherein the optical modulation element and the photoelectric conversion material are provided between By applying a voltage to a pair of intervening electrodes and irradiating the photoelectric conversion material with light information including gradation information, the voltage applied to the optical modulation element changes with time according to the gradation information. Modulating the time from the transition of the optical modulation element from the first stable state to the second stable state to the transition of the optical modulation element from the second stable state to the first stable state, A method of driving an optical modulation device, wherein a maximum value of the time period set is set shorter than a predetermined period so that a change in gradation level can be recognized. 17. A method of driving an optical modulator having a light source and an optical modulator including an optical modulator and a photoelectric conversion material, wherein a pair of optical modulator and the photoelectric conversion material are interposed therebetween. By applying a voltage to the electrodes and irradiating the photoelectric conversion substance with light information including gradation information, the voltage applied to the optical modulation element changes with time according to the gradation information, whereby the optical modulation element is changed. Modulates the transition from the first alignment state to the second alignment state, and sets the maximum value of the lighting time of the light source to be shorter than a predetermined period so that the change in the gradation level can be recognized. Driving method of optical modulator. 18. A method of driving an optical modulator having a light source and an optical modulator including an optical modulator and a photoelectric conversion material, wherein a pair of optical modulator and the photoelectric conversion material are interposed therebetween. A voltage whose polarity is reversed and a DC component is substantially zero is repeatedly applied to the electrodes, and the photoelectric conversion substance is irradiated with optical information including gradation information, and the optical modulation is performed according to the gradation information. By changing the voltage applied to the element over time, the timing at which the optical modulation element transitions from the first alignment state to the second alignment state is modulated, and in either the first half or the second half of the predetermined period, A method for driving an optical modulator, which comprises turning on a light source. 19. The method for driving an optical modulation device according to claim 15, wherein the optical modulation means is an element in which the optical modulation element and a photoelectric conversion substance are arranged between a pair of electrodes. 20. The method of driving an optical modulator according to claim 14, wherein the optical modulator is an element in which an optical modulator having a memory property and a non-single crystal semiconductor are arranged between a pair of electrodes. 21. The method of driving an optical modulator according to claim 14, wherein the optical modulator is an element in which a chiral smectic liquid crystal and a non-single crystal semiconductor are arranged between a pair of electrodes. 22. The method of driving an optical modulator according to claim 14, wherein the light modulator is an element in which a chiral nematic liquid crystal and a non-single crystal semiconductor are arranged between a pair of electrodes. 23. The light modulation means is an element in which a ferroelectric liquid crystal and an optical conversion substance are arranged between a pair of electrodes.
A method for driving the optical modulator according to any one of 4 to 18. 24. The method of driving an optical modulation device according to claim 14, wherein the light modulation means is an element in which an optical modulation substance and non-single crystal silicon are arranged between a pair of electrodes. 25. The method of driving an optical modulator according to claim 14, wherein the optical modulator is an element in which an optical modulator and a non-single crystal silicon germanium are arranged between a pair of electrodes. 26. The method of driving an optical modulator according to claim 14, wherein the light source starts lighting in synchronization with the start of application of a write voltage after reset. 27. The light source is turned off before the transition from the second alignment state to the first alignment state.
8. A method for driving the optical modulator according to item 8. 28. The light source is turned on only for a time corresponding to a modulation time range of a timing at which the optical modulation element transits from the first alignment state to the second alignment state.
8. A method for driving the optical modulator according to item 8. 29. When the grayscale level of the grayscale information is minimum or maximum, the light source starts lighting in synchronization with the start of application of a write voltage after reset, and the light source starts from the first alignment state. The method for driving the optical modulator according to claim 14, wherein the light is turned off before the transition to the second alignment state. 30. When the grayscale level of the grayscale information is maximum or minimum, the light source starts lighting in synchronization with the start of application of a write voltage after reset, and the light source starts from the second alignment state. First
The method for driving an optical modulation device according to claim 14, wherein the light is turned off before the transition to the alignment state. 31. A cycle in which the light source is repeatedly turned on is shorter than a cycle corresponding to a flicker frequency.
A method for driving the optical modulation device according to. 32. The light source according to claim 14, wherein the light source is a light source for sequentially and selectively irradiating light in different wavelength ranges, and the cycle of repeated lighting of the light source is shorter than the cycle corresponding to the flicker frequency. Driving method of optical modulator. 33. The applied voltage applied to the optical modulation means is a voltage whose polarity is inverted and a DC component is substantially zero within a predetermined period, and the light source is lit for a period shorter than the predetermined period. 18. A method of driving the optical modulation device according to any one of 18 to 18. 34. The method of driving an optical modulator according to claim 14, wherein the predetermined period or the continuous lighting period of the light source is 1/30 second or less. 35. The method of driving an optical modulator according to claim 14, wherein the continuous lighting period of the light source is 1/60 second or less. 36. The method for driving an optical modulator according to claim 14, wherein the predetermined period or the continuous lighting period of the light source is 1/90 second or less. 37. The continuous lighting period of the light source is 1/180
The method for driving an optical modulation device according to claim 14, which is a second or less. 38. The light source is a white light source.
18. A method of driving the optical modulation device according to any one of 18 to 18. 39. The method of driving an optical modulator according to claim 13, wherein the light source is a light source that sequentially emits red, blue, and green. 40. The method of driving an optical modulator according to claim 13, wherein the applied voltage applied to the optical modulator is a voltage whose polarity is inverted and a DC component is substantially zero within a predetermined period. 41. The applied voltage applied to the optical modulation means is a voltage whose polarity is inverted and a DC component is substantially zero within a predetermined period, and the applied voltage is applied at a cycle corresponding to a flicker frequency. A method for driving an optical modulator according to claims 13 to 18, which is shorter. 42. The method of driving an optical modulator according to claim 13, wherein a reset voltage is applied to the optical modulator. 43. The optical information including the gradation information is applied to the optical modulating means in synchronization with the application of a write voltage applied to the optical modulating means after resetting.
A method for driving the optical modulation device according to. 44. The optical information including the gradation information is supplied to the optical modulation means in synchronization with an application period of a voltage having the highest crest value in a writing voltage application period applied to the optical modulation means after resetting. The method for driving the optical modulation device according to claim 13, wherein irradiation is performed. 45. The optical modulation means is irradiated with the optical information including the gradation information only in the first period of the write voltage application period applied to the optical modulation means after resetting. A method of driving the described optical modulator. 46. The optical information including the gradation information is applied to the optical modulation means only in a first period of a writing voltage application period applied to the optical modulation means after reset, and thereafter, the writing voltage is applied. Is gradually changed.
18. A method for driving the optical modulator according to item 18. 47. A method of driving an optical modulation device according to claim 13, wherein the optical modulation means is irradiated with optical information including the gradation information and bias light which does not depend on the gradation information. 48. A method of driving an optical modulation device according to claim 13, wherein after irradiating the optical information including the gradation information, the bias light which does not depend on the gradation information is irradiated to the optical modulating means. 49. Before irradiation of light information including the gradation information,
14. A reset voltage is applied to the optical modulation means.
18. A method for driving the optical modulator according to item 18. 50. Before irradiation of light information including the gradation information,
The method for driving an optical modulator according to claim 1, wherein a reset voltage is applied to the optical modulator, and bias light that does not depend on the gradation information is applied to the optical modulator. 51. The method of driving an optical modulator according to claim 14, wherein an irradiation period of the light information including the gradation information and a lighting period of the light source are different. 52. A method of driving an optical modulation device according to claim 14, wherein a voltage applied to said light modulating means at the time of irradiating said light information including said gradation information is made different from a voltage applied after said irradiating. 53. The method of driving an optical modulator according to claim 1, 13, or 14, wherein the maximum duty of modulated overlap time is equal to or less than ½. 54. The maximum duty of the modulated overlap time corresponding to each color is 1/6 or less.
13. A method for driving the optical modulation device according to 13, 14. 55. The method of driving an optical modulation device according to claim 1, wherein the optical modulation element is a reflector having a variable anti-slope direction. 56. An optical modulation element having a photoconductive layer and an optical modulation element arranged between a pair of electrodes to which a voltage is applied, a signal light source for giving optical information including gradation information to the photoconductive layer, In a driving method of an image display device having a reading light source for giving reading light for reading image information to an optical modulation element, a lighting time is controlled so that the reading light source is lit in a period different from a period in which the optical information is given. Then, the driving method of the image display device, wherein the overlapping time of the lighting time and the time in which the optical modulation element is in a predetermined optical state is modulated according to the gradation information.